The invention relates to engine analyzers for internal combustion engine direct ignition systems and, more particularly, to engine analyzers employing ignition signal pickups to detect ignition waveforms in direct ignition systems. The invention has particular applicability to automotive engine analysis in which ignition waveforms are displayed for technician evaluation.
Engine analyzers provide mechanics with a tool for accurately checking the performance of the ignition system as a measure of the overall engine performance. Signal detectors (xe2x80x9ctest probesxe2x80x9d) are widely used in diagnosing defects and anomalies in internal combustion engines. A test probe is, for example, placed adjacent a test point such as a ignition coil, and the test probe communicates the signal back to a motor vehicle diagnostic apparatus. Information obtained from the test probe, such as spark plug firing voltage and duration, can help a mechanic determine if a spark plug associated with the ignition coil is functioning properly.
FIGS. 1a and 1b illustrate, respectively, the relationship between a typical primary ignition waveform and secondary ignition waveform as a function of time. The waveforms have three basic sections labeled Firing Section, Intermediate Section, and Dwell Section. Common reference numerals are used in FIGS. 1a and 1b to represent common events occurring in both the primary and secondary waveforms. As shown in FIGS. 1a and 1b, at the start S of the waveform, no current flows in the primary ignition circuit. Battery or charging system voltage available at this point is approximately 12-15 volts. At 10, the primary switching device turns on the primary current to start the xe2x80x9cdwellxe2x80x9d period. At 20, current flows through the primary circuit, establishing a magnetic field in the ignition coil windings. A rise in voltage occurs along 30 indicating that coil saturation is occurring and, on ignition systems that use coil saturation to control coil current, a current hump or voltage ripple appears at this time. The part of the waveform representing primary circuit on-time is between points 10 and 40. Thus, the portion of the signal between points 10 and 40 represents the dwell period (cam angle on breaker point ignition systems) or xe2x80x9con-timexe2x80x9d of the ignition coil primary current.
The primary switching device stops the primary current flow at 40, suddenly causing the magnetic field that had built up to collapse and induce a high voltage in the primary winding by self-induction. An even higher voltage is induced, by mutual induction, into the secondary winding, because of a typical 1:100 primary to secondary turns ratio. The secondary voltage overcomes the resistances in the secondary circuit up to the spark plug gap. The spark plug gap is ionized and current arcs across the electrodes to produce a spark 50 (i.e., the xe2x80x9cfiring linexe2x80x9d) to initiate combustion. During the xe2x80x9cspark linexe2x80x9d 60, the actual discharge voltage across the air gap between spark plug electrodes is reduced until the coil energy is no longer able to sustain the spark across the electrodes (see e.g., 70). At 80, an oscillating voltage results. Oscillations in the primary circuit occur until, at 90, the coil energy is dissipated and there is no current flow in the primary circuit.
In early ignition systems, such as the ignition system for a four cylinder engine illustrated in FIG. 2, a single ignition coil 120 is connected to one spark plug (e.g., 150) at a time by a distributor 130. Ignition coil 120 is essentially a transformer which transforms the low voltage in the primary winding provided by battery 100 to a high voltage in the secondary winding. The high voltage current pulses generated in the secondary winding are routed to distributor 130, which selectively routes the high voltage pulses to selected spark plugs (e.g., 150). As is well known, at each cylinder, the resulting electric discharge between the spark plug electrodes produces a spark which ignites a fuel-air mixture drawn or forced into the cylinder and compressed to an explosive state, thereby driving a piston in the cylinder to provide power to an attached crankshaft. Analysis of ignition waveforms to evaluate engine performance is performed by capacitively coupling a waveform signal pickup 140 to the coil 120 or a spark plug wire, for example.
More recently, ignition systems have evolved to one coil per cylinder, and may not have any spark plug wire at all. So called xe2x80x9cdirect ignitionsxe2x80x9d incorporate an ignition coil over each plug or an ignition coil near each plug. In xe2x80x9ccassette typexe2x80x9d spark ignition systems, the ignition coils are disposed directly over the cylinders. An example of a direct ignition coil is shown in FIG. 3. High voltage generated at the secondary coil 340 by means of the primary coil 320 and magnetic core 300 is routed through the output 330 of the secondary coil to conductive shaft 360 and to the spark plug 380. Thus, there is one ignition coil per spark plug.
In general, there is a wide variation of ignition coil architecture, placement, and interconnection among different manufacturers and vendors. Accordingly, it is difficult to standardize a pickup for measuring ignition waveform and it is often necessary to obtain different clip-on arrangements for coupling the pickup to a coil for different manufacturers. There are approximately 26 styles of coils for direct ignition systems used by 19 vehicle manufacturers. This variation in ignition coil architecture, placement, and interconnection among manufacturers results in significant variations in ignition output waveforms and signal intensities. Signal analysis is further complicated by use of after-market coils, which may exhibit stronger or weaker signals than OEM coils. Presently, secondary ignition coil waveform analysis is performed using a multitude of secondary ignition coil testers often configured for specific makes and models of automobile engines.
Correspondingly, a method and apparatus to measure and display ignition coil waveforms, particularly secondary ignition coil waveforms, for a variety of makes and models of automobile engines is needed. A simplified set of testers is needed to reduce the arsenal of testers currently required down to a manageable number of essentially universal ignition waveform pickups. An electronic circuit interface between the simplified set of testers and an engine analyzer and display device, such as a Sun machine version 4.0 is also desired to condition and amplitude normalize the waveforms. In this respect, commonly used handheld electronic diagnostic device provide only a histograph or other simplified representative of selected sample points, such as a sampling of the maximum voltage per revolution of the engine, and are not suitable for complete waveform analysis.
In one aspect, a coil-over-plug testing adapter system for use in combination with an engine analyzer is implemented with a capacitive pickup probe. The adapter system also includes an input port arranged to receive a signal provided by the capacitive pickup probe when placed in proximity to a coil-over-plug or coil-near-plug ignition assembly under test and a gain controller configured to modify a signal developed at the input port selectively by amplification and/or attenuation. A trigger pickup is arranged to provide, if needed, a timing signal from the coil-over-plug or coil-near-plug assembly to the engine analyzer. An output port is arranged to output the signal modified by the gain controller to the engine analyzer.
In another aspect, a method of displaying ignition coil waveforms includes disposing a plurality of capacitive elements adjacent a plurality of coil-over-plug ignition coils and selecting on an adapter electrically connected to the capacitive elements at least one of a predetermined gain, polarity, and range according to a vehicle under test. Ignition coil signals are measured and transmitted to the adapter, where they are conditioned according to the selected predetermined gain, polarity, and/or range are output from the adapter and displayed.
Yet another aspect provides a capacitive ignition coil probe comprising a substantially planar first conductive layer, a substantially planar second conductive layer, and a dielectric layer between the first conductive layer and second conductive layer. An insulating material laminates the first conductive layer, the second conductive layer and dielectric layer which form, in combination, an elongated flexible capacitive bar.
Still another aspect provides a capacitive ignition coil pickup set comprising a plurality of probes including a substantially planar first conductive layer and a substantially planar second conductive layer separated by a dielectric layer and laminated by an insulating material, a conductive path connecting the probes. Further included are a first connector at a distal end of the conductive path and a second connector at a proximal end of the conductive path. The probes are spaced apart from one another a predetermined distance along the conductive path and a distance between each of the first connector and second conductor to a respective adjacent probe is approximately one-half the predetermined distance between adjacent probes.